Pulse echo radar system employing a double channel



April 20, 1954 s, P N N 2,676,317

PULSE ECHO RADAR SYSTEM EMPLOYING A DOUBLE CHANNEL Filed Jan. 12, 1945 3 Sheets-Sheet 1 CIRCUIT INDICATOR SWEEP INVENTOR 1 ELLISON s. PURINGTON.

- RNEY NEL April 20, 1954 s. PURINGTON PULSE ECHO RADAR SYSTEM EMPLOYING A DOUBLE CHAN 3 Sheets-Sheet 2 Filed Jan. 12

.EDUmZU l .CauEu 53m 32.526 a 5.2;: 2 min...

muZuuum INVENTOR ELLISON S. PURINGTON.

April 20, 1954 E. s. PURINGTON 2,676,317

E CHANNEL PULSE ECHO RADAR SYSTEM EMPLOYING A. DOUBL Filed Jan.

3 Sheets-Shget 3 i muuuum Patented Apr. 20, l954 UNITED STATES PATENT I o FicE PULSE ECHO RADAR SYSTEM EMPLOYING A DOUBLE CHANNEL Ellison S. Purington, Gloucester, Mass, assignor, a by mesne assignments, to Radio Corporation of America, New .Xork, N. Y.,.- a corporation #of Delaware r "Application January 12, 1945, Serial No. 572,496

' '8 Claims. (Cl. 343-43) This invention relates to a system for deter- The radiant energy waves from the transmitmining the distance from or height of an object ters II and I4 after reflection from a distant and has for an object to provide a novel and object, indicated at H, are received by receiving improved system of the above type which is caantennas l8 and I9 which are connected to repable-of working through interference. ceivers 20 and 2! respectively tuned to the fre- Anotherobject isto provide a system of the quencies f1 and fraud selective of those freradar typewhich cannot be interfered withv by quencies. The pulses produced by the transmitthe enemy even when the object being measured ters l I and M are selected and made available in isitself-equipped-with radar.- the respective output circuits of the receivers accordance withthe present invention, the m 20 and 2|. radar signals are" propagated in the form of The receivers 20 and 2! are connected to a copulses ontwo difierentchannels and with a preincidental keycircuit 23, a delaycircuit 22 being determined pulse sequence.- Tne receiver for the interposed between the receiver 20 and the key reflected? waves respond only to received pulses circuit 23 and .so adjusted that the delay introof the predetermined sequence. The timing of duced by the circuit fl zicorresponds.to. that introthe= received-pulses with-respect .to the transduced by the circuit 13- of the transmitter and mittedpulses,-whichis a measure of the distance will cause the two pulses received .to arrive at to-the objectisdetern'iinedzby a standard indithe coincidental key circuit .23 simultaneously. catorsuch as a:.-cathode ray tube or oscilloscope. The coincidental :key circuit 23 is designed to Meansare provided for controlling at will the 20 respond only to the simultaneous reception of the pulser sequence both of the transmitter and of two pulses and produces a signal which is supplied the receiver so :that. in the case of interfering to the signal input circuit of an indicator 16 such signals-the pulse. sequence may be changed to as a cathode raytube. The input to thetranseliminate the. interference. As the system is only mitter I4 is connectedwto the sweep input circuit responsive to the predetermined pulse sequence 2 0f the indicator d is adapted to Cooperate spurious indicationsare largely eliminated. with the signal "input C c to produce an ?Ihe invention will be better understood by redication which represents the distance travelled ferring'tothe followingdescription, taken in conby the reflected waves as is well known in the nection with the-accompanying. drawings in which radar art. certain specific embodiments thereof have been m n th syst m. no ind ti n u ts m pu s set;forth.for purposes of illustration. 011v a singlefihannelras n the usua radarand uIn: the-drawings, V altimeter devices. Operation results only from Fig. -1 is a schematic block diagram illustrating th o jo t oper ti n Ofpulses. on the diflerent the present inv ntion; channels with a time, delay between pulses which is preset by devices 13 and 22. If the object I! is itself transmitting radar pulses, this will not -.Fig..:2 is a-schematic diagram of a transmitting and receiving circuit illustrating one embodiment of the invention; and be a, source or disturbance. Even if the types of Fig. :3 is a similarschematic diagram illustratqu pment ar t a e; interference can be ing a further embodiment of the invention. avoided by simultaneous adjustment of the two .=Referringto Fig. 1, the transmitter and receiver delays l3 and 22 so as to makethe system-reare-ofthegeneral type disclosed in my co-pendsponsive to difierent time. delay intervals on the ing application Ser. 537,799, now Patent No. two channels than is being used by the similar 2,449,819; issued September 21, 1948, filed May 29, equipment on the object l7. 1944, forRadioControl System and embodies a In Fig. 2, 'elements which correspond to those pulse-formingcircuit'lll which iscapable of form- 'of Fig. i 1 are given similar reference numbers. ingwa seriesof {short pulses and is connected to The delay devices l3 and 22 of Fig. 2 are of the modulate transmitters l! and M operatingretransmission line type, it being understood that spectively on frequencies .71 and-f2 andprovided several sections can be used between taps. he With radiating antennas l2 and I5 respectively. variation of time delay is accomplished by choice A delaynircuit l3-is connected between the pulse 0 of the output tap of the delay device, and this forming-circuit I D and the input to the transmaybe made unicontrol if desired. .The indimitten. ..-so ;as to introduce apredetermined cator is of the cathode ray tube type and includes delay in-the pulse modulating. the-transmitter I4 a sweep circuit energized by pulses from the so that the-transmitters H and M are pulsed in input of transmitterl4; and a grid control cirsequence lwltlrapltedetermined, interval between 55 cuit energized fromthe coincidental key circuit. pulses. 1 If The sweep circuit comprises input condenser 30 the output of which is connected to one grid of duo-triode tube 3|, which in turn is connected through resistor 32 to the positive end of battery 33, the negative end of which is connected to ground line 34. This tube is powerized from batteries 36, 31, 38 connected in series, with the negative end of 36 connected to the ground line 34 and the positive end of 38 connected to plate supply line 39, from which the plates of both triodes of 3| are connected by resistor 48. The negative end of a battery 4| is connected to the junction of the resistor 32 and the battery 33, and the positive end of the battery 4| is connected to the cathodes of both the triodes of tube 3|. The plates of tube 3| are connected through blocking condenser 42 to the two grids of a duo-triode tube 43, which in turn are connected to the ground line 34 through a resistor 44. The cathode of one of the triodes 43 is connected to ground, and its plate is connected through resistor 45 to plate supply line 39, and through resistor 46 to the second grid of 3|, which in turn is connected through resistor 41 to ground line 34. The remaining cathode of tube 43 is connected to the positive end of battery 48, the negative end of which is connected to ground line 34, and the corresponding plate is connected through resistor 49 to the plate supply line 39, and also to a horizontal deflection plate 50 of an oscilloscope tube 5|, the other deflection plates 53, 54, 55 of which are connected together and to the junction of batteries 3'! and 38, and also to the oscilloscopeaccelerating anode 56. The oscilloscope is provided also with a focusing electrode 51, control grid 58, cathode 59, with heater 68. The positive side of battery 6| is connected to ground line 34, and the negative side is connected to the focusing electrode 51 and to the positive side of a battery 62, the negative side of which is connected to the cathode 59, and to the positive side of a battery 63, the negative side of which is connected through a resistor 64 to the control.

rid 58.

The coincidental key circuit 23 comprises a duotriode tube 65, the cathodes of which are connected to a ground line 66. One grid of tube 65 is connected to the output of the delay device 22 and the other grid is connected to the outputvof the receiver device 2|. Athree section battery 61, 68, 59 is connected with the negative end to ground line 66, and positive and to plate supplyline 10. The plates of tube 65 are connected together and through a resistor 1| to the plate supply line I0, also through resistor 12 to the grid of a triode tube '13 which in turn is connected through resistor 14 to ground line 66. The cathode of tube 13 is connected to the junction of batteries 61 and 68. The plate of tube.'|3 is connected through a resistor 15 to plate supply line and is connected, through a condenser 13 to the grid-of a triode tube 11, which in turn is connected to the ground line through condenser 18 and resistor 19 in parallel. The cathode of tube 11 is connected to ground line 66, which in turn is connectedby ground line 88 to ground line 34. The plate of tube 11 is connected through resistor 8| to .plate supply line Ill, and through a condenser 82 to the control grid 58 of the oscilloscope 5|. The face of the oscilloscope is provided with a suitable scale 83 which may be calibrated in terms of the electrical path length from antenna l5 to antenna [9 by way of the refiectingobject l-l not shown.

It will be understood that the filaments of the tubes are heated by devices not shown, that the delay devices l3 and 22 are similarly set, as at position 3, and that a reflecting object I! is in position to render the system operative. In place of batteries shown for simplicity, suitable other sources of D. C. voltage may be used.

In the operation of the device, the pulse forming circuit l3 recurrently produces a positive pulse which amplitude modulates the transmitter H, causing energy of a short duration to be radiated from antenna l2. This energy is propagated to distant object i1, is reflected back, received by antenna l8, selectively actuates receiver 20 which produces a negative pulse which enters the delay line 22 and is delayed by a time interval corresponding to three sections thereof, and is impressed upon one grid of tube 85.

The positive pulse produced by circuit II) also actuates delay device l3 and is delayed by a time interval corresponding to three sections thereof. Part of the output pulse of amplitude modulated transmitter it, causes radiation from antenna |5, propagation to object li, reflection back to antenna I9, selective reception and detection by receiver 2|, to cause a negative pulse impressed upon the other grid of tube 65. Since the total path delays from pulse forming circuit In to coincidental key tube 65 are equal, the pulses arrive at the two grids of 65 at the same time.

The remaining part of the positive pulse output of delay device 13 is impressed upon the actuating grid of tube 3|. This tube is provided with suflicient positive cathode bias so that in the steady state condition with no pulse impressed, there is little or no current flowing to the plates through resistor 43, whereby the plates of the tube 3| are substantially at the potential of plate supply line 39. When the positive pulse is impressed through condenser 30 upon the grid of tube 3|, the corresponding plate momentarily draws current, driving the potential of both ends of condenser 42 negative; and driving the grids of tube 43 negative. This cuts oil. plate current a through resistor 45 and increases the current through resistors 46 and 41, and brings the grid of the second portion of tube 3| sufiiciently high so that current continues to pass through resistor 40 after the controlling pulse through condenser 30 has passed. The triodes of tube 43 are so constructed and the battery 48 so chosen that while the pulse through 42 drives the grid of the first section far beyond cutoff, the plate resistor 49 of the other section passes current at all times. After the pulsing of tube 43, the condenser 42 discharges toward the equilibrium condition with ever diminishing current through resistor 44 and decreasing potential on the grids of the tube 43, and continuously changing current through resistor 49. This action continues until plate current passes through resistor 45 cutting ed the second portion of tube 3|, and rapidly bringing the grids of tube 43 to equilibrium condition, in which they remain until the system is again pulsed. Thus the current through 49 is changed at the pulse rate, with a useful portion of the cycle of operation at slow speed determined by the time constant or discharge operation of condenser 42 and associated networks. During this useful portion, the potential of oscilloscope plate 50 is diminishing in accordance with the increasing current through resistor 49. The batteries 31 and 38 are so chosen that at the start of the useful portion of the sweep, the plate 50 is positive with respect to plate 53, so that any oscillopulsed-positively due to the vreception of pulsesfromlthelobject l1, and a scale may be provided calibratedso' that the spot of lighten the screen willdndicatethe distance of the object l7.

ufl hecoincidental key circuit 23 which controls the operationof-thelgrid 58 to cause the spot f light-to exist operates only when both grids 0f duo-triode tube- 65 are negatively pulsed-at the same --time. --=The direct I coupling from these triodes :to-triode ='l3- isso arranged-that the absence -:of pulses, no current passesthrough resist0r;'|5.-- -M0reover' the bias of tube 13" is such that if one'of-the triodes 3 of 65 is pulsed, 'noplate current of tube v 15 results. With triodes ot--65 for example of =10;000 ohms impedance at normal zero grid voltage, the circuits maybeso ad-' justed- -t'hat tube -13 passes current only when the impedance of the triodes of- 65 in parallel exceeds a high predetermined amount, "say 200 000 ohms, which can be accomplished'only when both grids of tube 65 are simultaneously pulsed-negatively.

'--The si-multaneous application of negative pulses to both grids-of tubefi therefore produces asingle-negative pulse on the plate of triode' 13.

which is transferred through condenser 76 to the grid=oi thephase invertin amplifier triode I1. The condehser-Hi and resistor 19 may be proportioned to give a pulse on'the grid. of tube 7'! of somewhat longer duration than the pulses on grids; oi tube- 65, so that the spot ofthe oscilloscope will be suitably illuminated for best operation.-- The negativepulse on the grid of tube 11 produces a positive pulse onthe'plate of'tube TL'WhiOh is transferred throughcondenser' 82 to pulse the control grid 58 0f theoscilloscope in a positive sense to cause illumination of the oscilloscope screen at ascaIe point corresponding to the time delay of the system due to the e e alpet In the modified form of Fig. 3,. the principles of operation in general are the same as for Fig."

2 'eigceptthat a circular sweep isus ed to give a somewhat longer calibrated scale for a given size oscilloscopethan possible with a linear seale, and to provide other improvements in" operation.

Since a circular sweep is most easily'developed from asirie wave generator, itis more practical to supply the oscilloscope sweep from a point in the system'. prior tothe output of the transmitter delay l circuit. Therefore the pulse forming circuit is. here shown as comprising asine wave generator and a pulse generator ltl, with talge off irom between thetwo toasweep adjusting circuit l l0, and a sweep generator l3'01operatively connected to the oscilloscope I50; v The remaind r ringe is similar to that of Fig. 2 exi cept that the output of delay line I 3 is' used solely for operating the transmitterfl ljand corresponding parts have been given' similar referenee characters-.--- The elements 1GB and I 011 may be oi the type disclosed my copending 'applica tion Sen N0: 536;10 l, now Patent No. 2; 46j5}925, issued- March 29y 11949, filed May 18; 1944,"for Rad io Control System.

j The sweep adjuster is provided with input terminals ll l and-l l2 connected across'the output otsine wave generator I00, with a resistor-l l3 and-condenser H4 shunting the inputr- The terminals-H2 isconnected tola ground linei-l l5 and by s. ground lineal-l8 to the-ground of othenpar-ts- 7B" is half theeizternal path from the transmitter to.

the resistance of assembly H8 between inductor Ill and ground may be varied, 'andfwher eby a suitable'porticn of the voltage across resistor assembly 118 may 'be utilized. The taps on resistors Bland-l l9 and the input elements it, Ill'are so chosen that the output of'the sweep adjuster produces aphase delay corresponding to'the time delays of devices I3, 22, at corresponding choices of -taps, andso'thatthe output voltage ofthe sweep adjuster ii is independent of the-phase delay setting. All the adjustments of the sweep adjuster and the delay devices 13 and 22 mayibe made unicontrol as indicated by the dotted lines. The sweepgenerator comprises a triode tube Hi, the co'ntrolgrid of which is connected to a tap 3 of resistor H9, and the cathodeof which is grounded. The plate of tube 35 is connected through a resistor-134 to the positive end of a battery I33, the negative end of which" is grounded. The plate'of I3! is connected through a condenser l'35'to a phase shifting networkcomprising three arms in parallel, the other ends of the arms being connected to the positive side of battery I33. One of these arms ist'se'rve's' tore-4 arm comprises resistor l3! and condenser l38"in series, and a third arm comprises condenser I39 and resistor I40 in series. The 'numerical'i'mpedances of'eleme'nt's 131,. 38, 139, I l-ll are all equal at the frequency-oi operation of the generator I00.

The horizontal and vertical deflection plates l5l and I'52-0f oscilloscope are connected to the positive end of battery 133, the vertical defieotion plate IE3 is connected to the junction oi resistor l3? and condenser I 38, and the horizontal deflection plate l'54'is connected to the junction of condenser- I39 andresisto'r MB. The accelerating anode 5'6 of the oscilloscope is connected to the deflection plates HI and 52, and the other electrodes'are biased negatively with ground by batteries-l55p62', 63. g

Inv theoperationof Fig. .3, the output of the ,sweepadjuster is phase delayed by'th'e inductor and resistors H8 and H9 in parallel, with'the amount of delay increasing as the value of'the. resistor arm decreases- Since the voltage across by 45 degrees with respect to the voltage across resistor-36, the electric deflection field of the oscilloscope is'caused to' be rotary so, that if the grid '58 is sufficiently near cathode potential, a spot of light will appear on thescreen with'a circular sweep. 'A' circular'scale' may Ice-provided, calibrated substantially linearly 'with'distance around the scale, so that the appearance of the.

spot of light at a specific point of the scale will indicatedistance of the reflecting object I1, which respect to the receiver antennas. This indication will be independent of the setting of the control which ad- J'usts the time interval between pulses on the two channels which are required to operate the coincidental key circuit and cause the operation of the indicator.

In this manner, a system is provided in which the usual types of radar, and other sources of interference will not be capable of registering spurious indications, and withwhich similar systems may be prevented from interfering by choosing a difierent delay interval from that used by the interfering ystem.

While certain specific embodiments of the invention have been shown for purposes of illustration, it is to be understood that the invention is capable of various uses and that changes and adaptations may be made therein as will be readily apparent to a person skilled in the art. The invention is only to be limited in accordance with the scope of the following claims.

What is claimed is:

1. A distance measuring system comprising a pulse forming circuit producing a series of pulses, a pair of radiant energy transmitters connected to be modulated by said pulses to propagate radiant energy pulses over a pair of radio frequency channels, a delay circuit interposed between said pulse forming circuit and one of said transmitters tween the pulses on the respective channels, a pair of receivers selective of the respective channels to receive said pulses after reflection from an object, a, key circuit connected to the output of both receivers and responsive only to simultaneous pulses from both receivers, a delay circuit in the output circuit of the receiver responsive to the earlier pulse and suited to introduce a delay corresponding to that of said first delay circuit so that the pulses are made, concurrent at the key circuit When received in-the predetermined se pulses to said ObJGCt;

2. A distance measuring system comprising a Hike forming circuit forming aseries of pulses, a air of radiant energy transmitters-connected to )e modulated by said pulses to propagate radiant :1 object, a key circuit connected to the output f both receivers and "responsive only to simultneous pulses from both receivers, a delay ciriit in the output circuit of the receiver reonsive to the earlier pulse and suited to introme a delay corresponding to that of said first alay circuit so that the pulses are made con- Lrrent at the key. circuit when received in the edetermined sequence, indicator means actued by the conjoint action of said transmitters .d. said key circuit to indicate the distance welled by said pulses to said object, and means ecting a like adjustment of both of said der circuits for varying the pulse sequence.

3. A distance measuring system comprising a lse forming circuit forming a series of pulses, )air of radiant energy transmitters connected be modulated by said pulses to propagate liant energy pulses over a pair of radio fre- 5 channels, a pair of receivers selective of the respective channels to receive said pulses after reflection from an object, a key circuit connected to the output of both receivers and responsive only to simultaneous pulses from both receivers,

a delay circuit in the output circuit of the receiver-responsive to the earlier pulse and suited to introduce adelay corresponding to that of said first delay circuit so that the pulses are made concurrent at the key circuit when received in the predetermined sequence, and a cathode ray oscilloscope having a sweep circuit connected to respond to said transmitter and a signal circuit. connected to be actuated by said key circuit. to,

indicate the distance of travel of said pulses to said object.

4. A distance measuring system comprisinga pulse forming circuit forming a series of pulses, a pair of radiant energy transmitters connected to be modulated by said pulses to propagateradiant energy pulses over a pair of radio frequency channels, a delay circuit interposed between said pulse forming circuit and one of said transmitters to introduce a predetermined time interval between the pulses on the respective channels, a

pair of receivers selective of the respective channels to receive said pulses after reflection from an object, a key circuit connected to the output of both receivers and responsive only to simultaneous pulses from both receivers, a delay circuit in the output circuit of the receiver responsive to the earlier pulse and suited to introduce a delay corresponding to that of said first delay circuit so that the pulses are made concurrent at the key circuit when received in the predetermined sequence, a. cathode ray oscilloscope having a sweep circuit connected to respond to said transmitter and a signal circuit connected to be actuated by said key circuit to indicate the distance of travel of said pulses to said object, and means effecting like adjustment of both of said delay circuitsfor varying the pulse sequence at will.

5. A distance measuring system accordingv to claim 1 in which the key circuit comprises a pair of space discharge paths responsive to 'the respective receivers and output means responsive only to the simultaneous change of the space current in both of said paths.

6. A distance measuning system according to claim 3 in which the sweep circuit of the cathode ray oscillograph is pulsed in synchronism with the delayed pulse to cause a linear sweep of said ray. 7. A distance measuring circuit according 'to claim 3 in which the sweep circuit of said cathode ray oscillograph is responsive to a sine wave generator to produce a circular sweep of said ray and adjustable phasing means is provided to'adjust the sweep in accordance with the delay introduced by the delay circuits.

8. A distance measuring system com-prising 5 transmitter means for transmitting periodically recurring radiant energy pulses over a first radio frequency channel and for transmitting other periodically recurring radiant energy pulses over a'second radio frequency channel with said other pulses delayed a certain amount with respect to the first-mentioned pulses, the first-mentioned pulses and said other pulses recurring at the same repetition rate, receiver means for selectively re-.- ceiving the pulses of the first channel afterireflectionfrom an object and for selectively receiving the pulses of the second channel after reflection from said object, delay means supplied with signal from said receiver means for delaying the reflected first-mentioned pulses by said certain amount, coincident means responsive only to the application thereto of two pulses which are coincident, means for supplying to said coincident means the received second-channel pulses and the received and delayed first-mentioned pulses, and indicator means to which the output signal of said coincident means is applied and which is actuated by the cojoint action of said transmitting means and said coincident means to indicate the distance travelled by said transmitted pulses to said object.

References Cited in the file of this patent m Number UNITED STATES PATENTS Name Date Koch Oct. 10, 1939 Peterson Jan. 8, 1946 Seeley Aug. 6, 1946 Lawson Jan. 14, 1947 FOREIGN PATENTS Country Date Australia Mar. 19, 1939 

